The telecommunications industry traditionally has provided services to subscribers over narrowband circuits. These narrowband circuits provided acceptable performance when the bulk of the demand for telecommunications services was predominantly for voice traffic. In recent years, additional telecommunications services have been developed that can use much higher bandwidth, e.g., Internet access, video conferencing, corporate intranets. These "broadband" services are increasingly in demand. Unfortunately, the existing telecommunications networks are not designed to provide quality broadband services.
As the demand for access to telecommunications services increased, the industry used time division multiplexing technology to aggregate a number of lower bandwidth circuits onto higher bandwidth circuits. By the middle 1980's, the SONET standard was well established as a time division multiplexing technology for fiber optic transport systems. However, as anyone who has attempted to download a large data file over the Internet can attest, current broadband services do not operate well over the existing telecommunications infrastructure.
The telecommunications industry has been developing approaches that will allow better use of bandwidth in a broadband network. For example, Bellcore, with the assistance of others in the telecommunications industry, has provided standards for transmitting asynchronous transfer mode (ATM) packets over a SONET ring network. See, e.g., GR-2842 and GR-2837. These standards are incorporated herein by reference. These standards specify transmission of data between endpoints in a ring network over virtual circuits.
However, the standards do not speak to all issues relating to a ring network for carrying ATM traffic. First, the standards do not specify how to prevent a single point of failure from bringing down the network element and the network. Further, the standards do not address how to interconnect two sub-networks so that a single point of failure in one sub-network does not interfere with the operation of the second sub-network.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a ring network with virtual connections that survives single point of failure and that can interconnect with other ring networks without interfering with the operation of the other ring networks.